General retroreflection sheets have a laminate structure constituted with a surface protective layer, a mid layer as needed, and a reflective element layer. A method for achieving a desired retroreflective property has been known in which a large number of micro prisms are provided on one surface of the reflective element layer (hereinafter, may be also referred to as “prism type retroreflection structure”) as a means for achieving a retroreflective property.
For producing a reflective element layer having a prism type retroreflection structure (hereinafter, may be also referred to as “prism type retroreflective element layer”), a large number of micro prisms are formed on a film surface by carrying out thermal transfer to a flat film using a die for molding prisms. Thus, thermal transfer properties (prism formability) are required for materials that constitute a reflective element layer. Herein, the “thermal transfer property” means a performance required for forming micro prisms having a favorable shape by thermal transfer so as to enable the obtained reflective element layer to have a sufficient retroreflective property.
Conventionally employed materials that constitute a reflective element layer include polycarbonate resins in light of thermal transfer properties. However, polycarbonate resins are disadvantageous in terms of weather resistance. Therefore, a film constituted with an acrylic resin is laminated as a surface protective layer on a reflective element layer constituted with a polycarbonate resin to manufacture commercially products of retroreflection sheets that are favorable in weather resistance.
Also, when a prism type retroreflection sheet is industrially produced, it is necessary to cut a long prism type retroreflection sheet after the production to give an appropriate size; however, the micro prism on the surface of the sheet is likely to be an initiation point of a crack in the cutting, leading to a problem of ease in development of breakage of the sheet.
On the other hand, acrylic resins are advantageous in that they are superior in weather resistance and also superior in transparency, as is clear from use in the surface protective layers described above. However, acrylic films are disadvantageous in that upon application or attachment of the same on an undulatory substrate, breakage is likely to be developed at the resulting curved face portions.
In Patent Documents 1 and 2, an acrylic film that is superior in formability while securing transparency is reported, in which a crosslinked elastic acrylic resin is used. However, these documents merely investigate only formability upon in-mold molding, and thermal transfer properties are not in any way suggested. Still more, use of an acrylic resin as a component material of a reflective element layer having a prism type retroreflection structure is not also disclosed.